Users of Duets and now also Alligator boards running RepRapFirmware don't use a host program, because the web interface provides all that functionality and a lot more besides. See [reprap.org].

You still need to use a slicer to generate the GCode file. The most popular ones right now seem to be the Prusa edition of Slic3r, Cura, and Simplify3D. As you have to pay for Simplify3D and it doesn't seem to be improving as fast as the other two (which are free), I expect its popularity to decline.